Double-flooring panels presently available, described in a Japanese Laid Open No. S62-107044 for example, employs a technique of embedding threaded nuts around the bottom peripheries for the attachment of threaded support legs to the nuts. The separation height between the flooring panel and the foundation floor can be adjusted by rotating the leg component to change the section length which projects out from the flooring panel.
Such an arrangement is susceptible to loosening of the legs due to rotation of the legs caused by mechanical disturbance such as vibrations. To circumvent such problems, there have been attempts to prevent the leg rotation by means of additional component devices such as spring washers. In recent years, there have been attempts to eliminate such extra components by having elastically-loaded threads on the legs, as disclosed in Patent Gazette No. S56-19492, which are provided with slitted threads whose crests are slightly wider than those of the conventional threads. These threads prevent loosening of the support legs by the elastic spring-back action of the wider threads when threaded into regularly spaced threads of the receiving nuts in the flooring component.
This type of threading arrangement presents problems during on-site installation of the legs. That is, initial threading of the leg into the nut must be performed with care, because of a danger of threading into the opening of the split thread. If such cross threading is continued forcefully, it will cause tearing of the split crests, and ultimately lead to destruction of the threads on both nut and support leg, making further adjustments impossible. Therefore, the installation operation must be carried out with careful visual attention, and this is an undesirable factor which lowers productivity.